Sulphur abundances in disk stars: A correlation with silicon

We have performed new determinations of sulphur and silicon abundances for a sample of 26 disk stars based on high-resolution, high signal-to-noise spectra. The results indicate a solar [S/Fe] for [Fe/H] > −0.3, below which [S/Fe] increases to ~0.25 dex at [Fe/H] = −1.0. We find that there is a good correlation between [S/H] and [Si/H], indicating the same nucleosynthetic origin of the two elements. It seems that the ratio of sulphur to silicon does not depend on metallicity for [Fe/H] > −1.0. The implications of these results on models for the nucleosynthesis of a-capture elements and the chemical evolution of the Galaxy are discussed. Based on observations carried out at National Astronomical Observatories (Xinglong, PR China)

The lithium isotope ratio in the metal-poor halo star G271-162 from VLT/UVES observations

A high resolution (lambda /Delta lambda =~ 110 000), very high S/N (>~ 600) spectrum of the metal-poor turnoff star G 271-162 has been obtained in connection with the commissioning of UVES at VLT/Kueyen. Using both 1D hydrostatic and 3D hydrodynamical model atmospheres, the lithium isotope ratio has been estimated from the \ion{Li}{i},670.8 nm line by means of spectral synthesis. The necessary stellar line broadening (1D: macroturbulence + rotation, 3D: rotation) has been determined from unblended \ion{K}{i}, \ion{Ca}{i} and \ion{Fe}{i} lines. The 3D line profiles agree very well with the observed profiles, including the characteristic line asymmetries. Both the 1D and 3D analyses reveal a possible detection of \element[][6]{Li} in G 271-162, element [][6]{Li}/element [][7]{Li} = 0.02+/-0.01 (1sigma ). It is discussed if the smaller amount of \element[][6]{Li} in G 271-162 than in the similar halo star HD 84937 could be due to differences in stellar mass and/or metallicity or whether it may reflect an intrinsic scatter of \element[][6]{Li}/\element[][7]{Li} in the ISM at a given metallicity. Based on public data released from the UVES commissioning at the VLT/Kueyen telescope, ESO, Paranal, Chile

(Un)frozen spaces: Exploring the role of sea ice in the marine socio-legal spaces of the Bering and Beaufort Seas

Sea ice is a dynamic physical element of the greater Arctic marine system, one that has myriad connections to human systems on a variety of spatial and temporal scales. Changes to the spatial extent of sea ice simultaneously permits and endangers maritime operations, as well as impacts current debates over maritime boundaries, presenting an interesting challenge for international law. Sea ice is not a stationary object; it moves through time and space in response to the physical forces of wind, ocean currents, and heating. It has a tangible, material and substantive role in contestations over territory, resources and marine boundaries in both the Beaufort and Bering Seas. We suggest here that sea ice’s material nature in these marine regions continuously challenges stationary conceptions of law in complex and sometimes contradictory ways. Building on recent work on the human geographies of sea ice, the dynamic field of legal geography and recent contributions in ocean-space geography, we outline how the dynamism of sea ice could influence notions of boundary, resources and climate change in ocean-spaces of the greater Arctic region

O/Fe in metal-poor main sequence and subgiant stars

A study of the O/Fe ratio in metal-poor main sequence and subgiant stars is presented using the \ion{O{i}},6300 Å line, the \ion{O}{i} 7774 Å triplet, and a selection of weak \ion{Fe}{ii} lines observed on high-resolution spectra acquired with the VLT UVES spectrograph. The \ion{O{i} line is detected in the spectra of 18 stars with -2.4 < [Fe/H] < -0.5, and the triplet is observed for 15 stars with Fe/H ranging from -1.0 to -2.7. The abundance analysis was made first using standard model atmospheres taking into account non-LTE effects on the triplet: the \ion{O{i}} line and the triplet give consistent results with [O/Fe] increasing quasi-linearly with decreasing [Fe/H] reaching [O/Fe] =~ +0.7 at [Fe/H] = -2.5. This trend is in reasonable agreement with other results for [O/Fe] in metal-poor dwarfs obtained using standard atmospheres and both ultraviolet and infrared OH lines. There is also broad agreement with published results for [O/Fe] for giants obtained using standard model atmospheres and the \ion{O{i}} line, and the OH infrared lines, but the \ion{O}{i} lines give higher [O/Fe] values which may, however, fall into place when non-LTE effects are considered. When hydrodynamical model atmospheres representing stellar granulation in dwarf and subgiant stars replace standard models, the [O/Fe] from the \ion{O{i}} and \ion{Fe}{ii} lines is decreased by an amount which increases with decreasing [Fe/H]. These 3D effects on [O/Fe] is compounded by the opposite behaviour of the \ion{O{i}} (continuous opacity effect) and \ion{Fe}{ii} lines (excitation effect). The [O/Fe] vs. [Fe/H] relation remains quasi-linear extending to [O/Fe] =~ +0.5 at [Fe/H] = -2.5, but with a tendency of a plateau with [O/Fe] =~ +0.3 for -2.0 < [Fe/H] < -1.0, and a hint of cosmic scatter in [O/Fe] at [Fe/H] =~ -1.0. Use of the hydrodynamical models disturbs the broad agreement between the oxygen abundances from the \ion{O{i}} , \ion{O}{i}, and OH lines, but 3D non-LTE effects may serve to erase these differences. The [O/Fe] values from the \ion{O{i}} line and the hydrodynamical model atmospheres for dwarfs and subgiant stars are lower than the values for giants using standard model atmospheres and the \ion{O{i}}, and \ion{O}{i} lines. Based on observations collected at the European Southern Observatory, Chile (ESO Nos. 65.L-0131, 65.L-0507, and 67.D-0439)

Increased Incidence of Interatrial Block in Younger Adults with Cryptogenic Stroke and Patent Foramen Ovale

Background: Stroke is often unexplained in younger adults, although it is often associated with a patent foramen ovale (PFO). The reason for the association is not fully explained, and mechanisms other than paradoxical embolism may be involved. Young stroke patients with PFO have more atrial vulnerability than those without PFO. It is plausible that stretching of the interatrial septum may disrupt the interatrial conduction pathways causing interatrial block (IAB). IAB is associated with atrial fibrillation, dysfunctional left atria and stroke. Methods: Electrocardiogram (ECG) characteristics of prospectively recruited young patients (≤55 years of age) with unexplained stroke (TOAST and A-S-C-O) were compared with control data. All stroke cases underwent bubble contrast transthoracic and transoesophageal echography. IAB was defined as a P-wave duration of ≧110 ms. ECG data were converted to electronic format and analysed in a blind manner. Results: Fifty-five patients and 23 datasets were analysed. Patients with unexplained stroke had longer P-wave duration (p = 0.013) and a greater prevalence of IAB (p = 0.02) than healthy controls. Case status was an independent predictor of P-wave duration in a significant multivariate model. There was a significant increase in the proportion of cases with a PFO with IAB compared with cases without PFO and with controls (p = 0.005). Conclusions: Young patients with unexplained stroke, particularly those with PFO, exhibit abnormal atrial electrical characteristics suggesting atrial arrhythmia or atrial dysfunction as a possible mechanism of stroke

The BHK Color Diagram: a New Tool to Study Young Stellar Populations

A new method to derive age differences between the various super star clusters observed in starburst galaxies using the two color diagram (B-H) vs (H-K) is presented. This method offers a quick and easy way to differentiate very young and intermediate age stellar populations even if data on extinction are unavailable. In this case, discrimination of regions younger and older than 4 Myr is feasible. With the availability of data on extinction, the time resolution can be improved significantly. The application of the method to the starbursting system Arp 299 is presented. The validity of the method is confirmed by comparing the equivalent width of the H-alpha line with the chronological map of the northern part of NGC 3690.Comment: 32 pages, 7 figures, 1 table, AJ accepte

Thermalization of an anisotropic granular particle

We investigate the dynamics of a needle in a two-dimensional bath composed of thermalized point particles. Collisions between the needle and points are inelastic and characterized by a normal restitution coefficient $\alpha<1$. By using the Enskog-Boltzmann equation, we obtain analytical expressions for the translational and rotational granular temperatures of the needle and show that these are, in general, different from the bath temperature. The translational temperature always exceeds the rotational one, though the difference decreases with increasing moment of inertia. The predictions of the theory are in very good agreement with numerical simulations of the model.Comment: 7 pages, 6 Figures, submitted to PRE. Revised version (Fig1, Fig5 and Fig6 corrected + minor typos

100 Gbit/s real-time all-analogue filter bank OFDM based on a gain-switched optical comb

A real-time 5×21.6 Gbit/s WDM electro-optical transceiver is presented. Optical carriers were spaced by 20 GHz and each one transmitted four orthogonally overlapping broadband subcarriers. Only analogue electronics were employed, achieving an unprecedented spectral efficiency in DSP-less SCM links